Home made in cylinder transducer

I forgot all about that thread!
Thank you once again Matt, owe you a beer

I found the utility in Windows to test various functions of the scope, including the 5v power supply on the aux plug and was able to ID power and ground. I intend to re-pin the Snap-On rpm pick up too utilize it to power the transducer.

Mine isn't power all the time, so I don't know if it powers on when you select an appropriate test lead preset for a given channel or how it works yet.

I Also want to try a "wall wart" as you call it to see if it skews the 0 line compared to the USB ports on the Verus.

I downloaded the PDF and gave it a glance but I will give it a thorough read through this afternoon.

Once again, thank you very much!

Paul, I can't seem to get this to work for me.
I repinned an rpm pick up for the Verus to supply power and ground to my transducer but the calibration fails every time and the pressure ends up skewed very negative.
I have a couple that output 0.5 volts at atmosphere and it still won't take.

Do you use yours on the pressure setting or volts?

Very nice build by the way. I need some kind of coupler to thread mine into a compression gauge hose.

Pressure mode on the Verus and on the Vantage Pro, and it works every time.

So, some faultfinding is in order.

With the back removed from the d-type, plugged in to the diagnostic tool, with the pressure sensor soldered on, what voltages do you see on the relevant pins (as per the crap picture in my documentation)?

The Verus seems to expect a transducer that outputs 0.5 to 4.5v, with 0.5v for zero PSIG. When it does the 'calibration' thing, it's assuming that the transducer is electrically connected, but with zero pressure on it. This voltage is then deemed to be zero PSI by the Verus / Vantage Pro and 4.5v is full-scale (i.e. 500PSIG if you're in 500PSI sensor mode).

For adapting the transducers to a gauge hose do you know what thread diameter and pitch they are? And whether they're taper seal like a pipe thread or use a gasket or o ring?

Thinking back to when I built mine, both the transducer and the remains of the compression gauge kit were 1/4 NPT tapered thread. I just did the usual two wraps of PTFE plumber's tape that I do when fitting couplings to air-tools and it sealed up fine.

A lot are 1/4" Gas thread (more or the same as 1/4" BSP) as used on shop air compressors there is also a tapered version of this thread BSPT.
1/4" Gas looks very similar to 14mm spark plug thread but don't ever mix up the two types.

Also to clear up terminology a transducer is different from a sensor a sensor requires external power, a transducer dosen't require power it is two wire and generates its own voltage.

Aside from Brit and US pipe threads, which are different, there are also numerous other standard and metric threads Noahs transducers could be.

Andy.MacFadyen wrote: Also to clear up terminology a transducer is different from a sensor a sensor requires external power, a transducer dosen't require power it is two wire and generates its own voltage.

Three wire voltage output are transducers. 2 wire pressure transducers are usually 4-20 mA loop powered. I can't recall ever seeing one of those on a vehicle but they're the most common type for industrial process control.

www.omega.com/en-us/resources/pressure-t...cers-troubleshooting

The threads are small? Lol, not my bag. I never invested the time to learn threads...

I did find a brass coupler to marry it to my compression gauge but I think I'm abandoning the refrigerant pressure sensors.
The voltage output at rest is too low to use the pressure scale on the Verus. I ordered the same one (presumably) that Paul has had success with. The seller claims it to have a range of .5-5 volts.
All mine put out .012 at rest.
If faced with the prospect of spending several hundred dollars on a transducer set up, you better believe I'd just live with this setup on a 2v scale, measurement be damned. But for under $20, I'll give this a try.
Thanks for your help guys!

The 300psi sensor came in today. Hopefully there won't be too much work waiting for me Monday to try it out;)

The first testing with the new sensor is a bit disappointing. When compared to gauge pressure it is 5psi off (positive) around 5 psi and deviates proportionally as pressure increases. So 80psi gauge pressure is more than 100psi on the scope scale.

Looks like a proper 500psi & 100psi sensor is in order to properly use the pressure scale.

Is the sensor's update rate fast enough to deliver a good enough, not chopped waveform?
I got frustrated when playing around with these sensors because of the deficient resolution.

Could you upload a screenshot, please?

I never installed it in an engine after the bench test results were not favorable, but I should have something here at the shop I can get a waveform from and post it up.
It did seem to respond appropriately while changing the air pressure through my cylinder leak down tester, but obviously the changes taking place were not happening nearly as rapidly as inside a running engine.

For bench testing mine first I used a hand pump to confirm it would measure vacuum. Then threw together an airline quick connect Tee with a short hose from it to the transducer. Then hooked it up to a couple air hammers. The faster one is 4,500 BPM and the slower 2,500 BPM IIRC.

That's a pretty good idea to measure it's response, thanks Matt

I put it into my Ridgeline but unfortunately got occupied with visitors.

It did look like the sensor output at shorter time samples was choppy and not fluid, almost pixelated, but I was distracted. It could have been me...

After the clean captures from the salvaged refrigerant pressure sensors, I fully expected to see similar, nice, smooth transitions....

The sensor seems to have been damaged. It now outputs 1.5v at atmosphere and will not calibrate to use the voltage scale built into the Verus.

I do still have access to the Accord by the way. It's out in the yard with no tires, I just haven't had the ambition to go out there pull the head.

Noah wrote:
I do still have access to the Accord by the way. It's out in the yard with no tires, I just haven't had the ambition to go out there pull the head.

!!Go for it, Forest:) !!

Noah wrote: I do still have access to the Accord by the way. It's out in the yard with no tires, I just haven't had the ambition to go out there pull the head.

If it's past the point you can do any more running tests a cylinder leakdown test would probably be enough. That's if you can get compressed air out to it.

juergen.scholl wrote:
!!Go for it, Forest:) !!

Matt T wrote:
If it's past the point you can do any more running tests a cylinder leakdown test would probably be enough. That's if you can get compressed air out to it.

Yeah, I regret not doing the leak down test before she was put out to pasture.
It likely still runs but is quite far away from an air line now, lol.

I've really got to start from scratch now with the failure of the sensor I was counting on using. Very disappointing.
I think it's worth it to revisit the refrigerant pressure sensor and try to develop a repeatable test procedure as far as scope set up is concerned, to gather accurate, interpretable information

I pulled the valve cover off the Accord this week and turned the engine with a ratchet out in the yard didn't see anything right away up top. I'm not looking forward to the support bracket that goes from the intake to the block. That's really the only hard part of doing it out in the yard.

Noah wrote: Yeah, I regret not doing the leak down test before she was put out to pasture.
It likely still runs but is quite far away from an air line now, lol.

I just experimented with my 4 gallon 125 psi compressor. With a 100% leak it took me 5 seconds to crank the reg up then I got 15 seconds run time before the inlet gauge started dropping. A 60% leak I got 20 seconds run time but it would probably be useable for finding where the leak was for a minute total. So if you've got a decent sized portable air tank might be worth carrying it out there.

Noah wrote: I think it's worth it to revisit the refrigerant pressure sensor and try to develop a repeatable test procedure as far as scope set up is concerned, to gather accurate, interpretable information.

They looked really good other than the inconsistency at atmospheric pressure. I think it's worth playing around with power supplies and 'scope settings to see if you can get that repeatable.